The induction of liver enzymes by cortisol after combined treatment of mice with X-irradiation and inhibitors of protein biosynthesis

RNA and protein synthesis of irradiated Ehrlich ascites tumour cells. II. Amount of m-RNA and in vitro investigations

Poly(A)-containing RNA (m-RNA) was studied in in vivo growing Ehrlich ascites tumour cells following a roentgen irradiation dose of 5 Gy. m-RNA increased significantly during the first 12 hours after irradiation. Thus, the observed decrease in protein synthesis rate during this time seems not to be due to radiation induced changes at the transcriptional level. The protein synthesis rate of in vivo irradiated cells incubated in vitro in culture medium was unchanged. On the other hand, the protein synthesis rate of non-irradiated cells incubated in vitro in ascites fluid from irradiated animals was decreased. We concluded that factor(s) inhibiting protein synthesis or the lack of factor(s) promoting protein synthesis in the ascites fluid is(are) of significance for the reduced protein synthesis of tumour cells found in irradiated in vivo growing cells.

Growth regulation in X-irradiated mouse skin; the possible role of chalones

Extracts of hairless mouse skin were tested for their content of epidermal G1 inhibitor and G2 inhibitor at daily intervals after X-irradiation with 4 500 or 2 250 rad. After either dose the skin extracts lacked G1 inhibitory activity on days 5 and 6 respectively after irradiation. This coincided with the time when the epidermal mitotic rate again became normal and started a period of over-shoot. The time interval of 5-6 days corresponds to the turnover time of the differentiating cells in hairless mouse back epidermis. The findings indicate that the proliferating cells in epidermis can respond to changes in local chalone concentration, even after X-irradiation at the tested doses, and that the irradiated epidermal cell population still retains some important properties inherent in a cybernetically regulated system. The local G2-inhibitory activity also varied after irradiation, but these variations could not be directly related to the corresponding mitotic rates.

Effects of ionizing radiation of RNA metabolism in cultured mammalian cells. III. Specific reduction in mRNA synthesis during resumed division and plateau phases following exposure to 800 rads of x irradiation

The cell growth response of cultured Chinese hamster ovary cells, line CHO, to 800 rads of X irradiation involves a period of division delay, followed by a period of resumed division which terminates in a plateau phase. Over 95% of the cells die eventually. No direct effects of RNA or protein metabolism are evident during the delay period. During the resumed division and beginning of plateau phases, however, a specific and relatively constant reduction in mRNA synthesis relative to messenger-like RNA and heterogenous nuclear RNA synthesis is evidenced. The ratio of mRNA to messenger-like RNA synthesis ranges from 0.8 to 0.65 during these phases. The effect is not due to altered cell-cycle distribution, and evidence is presented to indicate that it is probably not a compensatory response to the unbalanced growth that occurs during the division delay period.